G. Georgiev

Measurement and loss model of ferrites with non-sinusoidal waveforms

The usual data of commercial ferrite grades are given for sinusoidal waveforms, although the voltage in the typical applications in power electronics resembles to square waves. Firstly, an accurate two wire, oscilloscope power measurement is presented. Special wide frequency current and voltage transducers were designed, with a very low phase difference up to 50 MHz. Secondly, a ferrite loss model named natural Steinmetz extension (NSE) is presented. The model is checked with measurements on two different ferrite grades, with square waves with a large variation in duty ratio. The proposed model is compared with modified Steinmetz equation (MSE). The two methods with a different mathematical formulation give comparable but different results.

First Use of Post-Accelerated Isomeric Beams for Coulomb Excitations Studies of Odd-Odd Nuclei Around N=40

We report on the first use of post-accelerated radioactive isomeric beams. Long-lived isomeric states in 68Cu and 70Cu have been produced and separated at ISOLDE, CERN. Subsequently they were post-accelerated to 2.86 MeV/u and sent to a target in the center of the MINIBALL spectrometer, used for the detection of the γ-rays of interest. The preliminary results from the Coulomb excitation of the Iπ=6-, 1+ states in 68Cu and the Iπ=6- one in 70Cu, compared to a large-scale shell model calculations, hint the importance of the excitations across the Z=28 gap for the understanding of the nuclear structure in the neutron-rich N=40 region.

g-factor measurement of the 9/2+ isomeric state in 65Ni

We report on the first measurement of the g factor of the Jπ = 9/2+ isomeric state in 65Ni. (d,p) reactions on enriched 64Ni and 62Ni have been used in order to populate and spin orient the Jπ = 9/2+ isomeric states in 65Ni and 63Ni. The hyperfine field of the Ni target, oriented by an external magnetic field, was used in order to obtain a sufficient number of spin precessions within the relatively short life time of the isomers. The g factor obtained, g(65mNi) = −0.296(3), is in good agreement with the g factors of other 9/2+ states in the region and with shell-model calculations.

Implementation and evaluation of tilted foils polarization at REX-ISOLDE

The progress within atomic and nuclear physics relies on refining and adding new observables. One of these is the polarization of the nuclear spin, where there is a manifest interest in accessing a wide variety of polarized beams, e.g. at energies suitable for Coulomb excitation and transfer experiments. In particular, exotic nuclei with half-lives considerably less than one second are difficult to produce, but the issues present in traditional methods could be overcome by using the tilted foils technique. Two setups for measuring the degree of polarization of an ion beam after the REX-ISOLDE linear accelerator at CERN are being evaluated. An approach based on Coulomb excitation has been utilized in an experiment and preliminary results will be presented. Furthermore, a β-NMR setup is currently under construction that will take radioactive beams soon.

Sub-Barrier Coulomb Excitation of 106,108,110Sn

The reduced transition probabilities between the first excited 2(+) state and the 0(+) ground state, B(E2; 0(+) -> 2(+)), have been measured in Sn-106,Sn-108,Sn-110 using sub-barrier Coulomb excitation in inverse kinematics at REX-ISOLDE. The results are, B(E2;0(+) -> 2(+)) = 0.220(22),0.226(17), and 0.228(32) e(2)b(2), for Sn-110, Sn-108, and Sn-106, respectively. The results for Sn-106,Sn-108 are preliminary. De-excitation gamma-rays were detected by the MINIBALL Ge-array. The B(E2) reveals detailed information about the nuclear wave function. A shell model prediction based on an effective CD-Bonn interaction in the nu(0g(7/2),2s, 1d, 0h(11/2)) model space using e(eff)(nu) =1.0 e follows the experimental values for the neutron rich Sn isotopes, but fails to reproduce the results presented here. (Less)

Coulomb Excitation of Neutron-Rich Zn Isotopes: First Observation of the 2[sub 1][sup +] State in [sup 80]Zn

Neutron-rich, radioactive Zn isotopes were investigated at the Radioactive Ion Beam facility REX-ISOLDE (CERN) using low-energy Coulomb excitation. The energy of the 2(1)+ state in 78Zn could be firmly established and for the first time the 2+ --> 0(1)+ transition in 80Zn was observed at 1492(1) keV. B(E2,2(1)+ --> 0(1)+) values were extracted for (74,76,78,80)Zn and compared to large scale shell model calculations. With only two protons outside the Z=28 proton core, 80Zn is the lightest N=50 isotone for which spectroscopic information has been obtained to date. Two sets of advanced shell model calculations reproduce the observed B(E2) systematics. The results for N=50 isotones indicate a good N=50 shell closure and a strong Z=28 proton core polarization. The new results serve as benchmarks to establish theoretical models, predicting the nuclear properties of the doubly magic nucleus 78Ni.